Tricyclic antidepressant (TCA) overdose necessitating intensive care unit (ICU) admission remains a significant problem in the Western Cape. In this retrospective study, we reviewed the course of life-threatening TCA overdose in our centre to identify potential prognostic indicators. TCA levels >1 000 ng/ml were associated with QT and QRS prolongation and convulsions. However, no single parameter predicted non-survival. The overall mortality of TCA overdose was very low. Our findings should encourage clinicians to offer medical care including ICU admission, if necessary, to patients with TCA overdose.

Tricyclic antidepressants (TCAs) are widely prescribed for several indications in South Africa. Modes of action include presynaptic serotonin and noradrenaline re-uptake inhibition, antagonism of peripheral alpha-1-adrenergic receptors, a membrane-stabilising effect on the myocardium and anticholinergic action.1,2 Overdose may result in convulsions, neurological and respiratory depression and cardiac arrhythmias.2

The lifetime prevalence of major depression in South Africa is 9.7%.3 Depression is linked to suicide ideation with an average of 180 - 400 suicide attempts per 100 000 in the depressed population, compared with 10 - 25 per 100 000 in the non-depressed population.4 Other factors predisposing individuals to suicide attempts include female gender, physical illness, occupation and marital status.4

Despite South Africa's high prevalence of depression and wide use of TCA, we found no African study on TCA overdose. We describe the course of life-threatening TCA overdose in our centre to identify potential prognostic indicators.

Methods

In this retrospective analytical study, we reviewed admission records of the medical intensive care unit (ICU) and coronary care unit (CCU) of Tygerberg Academic Hospital from 1999 to 2008. Patients with a diagnosis of TCA overdose and a positive TCA level were included. The Health Research Ethics Committee of Stellenbosch University approved the study and the chief medical superintendent of Tygerberg Academic Hospital granted permission for anonymous data collection.

In total, 21 patients had high-risk ADORA scores. The mean APACHE II score was 12.4±9.0. The mean duration of ICU admission was 4.7 days (range 1 - 12); this did not correlate with the ADORA score, APACHE II score or TCA levels.

Three patients died (4.9% mortality); 2 from complications related to aspiration pneumonia and 1 from refractory shock secondary to concomitant beta-blocker overdose. The ADORA score, APACHE II score or TCA levels failed to predict these cases.

Discussion

We found a very low mortality rate with TCA overdose, consistent with a study from Iran.6 Remarkably, no patient died from cardiac arrhythmia or other direct toxic sequelae of the TCAs, despite a higher incidence of QT prolongation and ventricular arrhythmias in the study population compared with most other studies.2,4,5-7 Therefore, clinicians working in resource-constrained healthcare systems should offer medical care including ICU admission, if necessary, to patients with TCA overdose.

Limitations of our study include its retrospective nature. In addition, only patients admitted to ICU or CCU were included; patients who may have died in the emergency room, en route to Tygerberg Hospital or before transfer from referring institutions were excluded. Therefore, the mortality of serious TCA overdose may be higher than observed.